Option Explicit
Private Declare Function SetWindowsHookEx Lib "user32.dll" Alias "SetWindowsHookExA" (ByVal idHook As Long, ByVal lpfn As Long, ByVal hmod As Long, ByVal dwThreadId As Long) As Long
Private Declare Function UnhookWindowsHookEx Lib "user32.dll" (ByVal hHook As Long) As Long
Private Declare Function GetPixel Lib "gdi32" (ByVal hdc As Long, ByVal x As Long, ByVal y As Long) As Long
Private Declare Function GetWindowDC Lib "user32" (ByVal hwnd As Long) As Long
Private Declare Function ReleaseDC Lib "user32.dll" (ByVal hwnd As Long, ByVal hdc As Long) As Long
 
Private Const WH_MOUSE_LL As Long = 14
 
Private Type POINTAPI
    x As Long
    y As Long
End Type
 
Dim hHook As Long
Dim lDC As Long
 
Public Sub StartHook()
    hHook = SetWindowsHookEx(WH_MOUSE_LL, AddressOf MouseProc, App.hInstance, 0)
    lDC = GetWindowDC(0&)
End Sub
 
 
Public Sub StopHook()
    Call UnhookWindowsHookEx(hHook)
    ReleaseDC 0&, lDC
End Sub
 
 
Private Function MouseProc(ByVal nCode As Long, ByVal wParam As Long, lParam As POINTAPI) As Long
    On Error Resume Next
 
    Dim lColor As Long
 
    lColor = GetPixel(lDC, lParam.x, lParam.y)
 
    If lColor = -1 Then
        ReleaseDC 0&, lDC
        lDC = GetWindowDC(0&)
        lColor = GetPixel(lDC, lParam.x, lParam.y)
    End If
 
    Form1.BackColor = lColor
 
End Function
 

Option Explicit
 
Private Sub Form_Load()
    StartHook
End Sub
 
Private Sub Form_Unload(Cancel As Integer)
    StopHook
End Sub